Infrared seeker systems are used in autonomous missile targeting systems for automatically selecting target objects in a cluttered background. Some munitions are free-falling aerodynamically steered vehicles having a small warhead which must be placed precisely on a target.
These missiles or munitions are small devices typically having a 5" diameter housing and approximately 100 cubic inch volume. Given their size, they must be able to process target data using a minimum amount of hardware so that it will fit inside the physical housing. However, the processor also must be fast enough to process the target information in only a few seconds as the missile or munition moves toward its target. In addition, since these vehicles are expendable the costs of the processor must be kept as low as possible.
There are three phases of the targeting process: acquisition, tracking and hit placement. Each phase relies on information from the previous phase of processing. This processing must be accurate at each phase because once the missile or munition is launched, no further communication with it is possible.
One problem with an infrared seeking system is that it can be difficult to discriminate between the target and background clutter. Clutter includes weather conditions such as fog, and the existence of countermeasures such as flares and jamming devices, all of which tend to obscure the desired target within the surrounding background. To reduce the effect of this problem, training data is collected on a variety of background terrain to provide image patterns which can help to guide the missile or munition. Given that any one location can experience a wide variety of weather conditions and that the training data for each weather condition also contains data associated with a specific target, the amount of training data required for accurate targeting quickly becomes too large for the missile or munition to sort and process in an appropriately short period of time.
Some weather conditions add to the confusion in being able to differentiate a target from something which is a part of the terrain. There may be times when certain environments emit an average background radiation level which is very close to that of a target. For example, a collection of rocks which have been in the sun at certain times of the day may be detected as hot spots and may be mistaken for targets.
Infrared seekers have also typically been designed to detect objects which are hot, for example, tanks which are currently operating. Cold targets such as tanks which have been sitting idle for a while and which have had time to cool off present a much more difficult problem for infrared seekers.